This proposal is directed towards extending our understanding of three key areas in chromosome biology. (1) We propose to study the nature and sites of histone phosphorylation in order to attempt to understand why histones are not phosphorylated to a significant degree in non-dividing cells, but are so modified when the cell is stimulated to divide. Utilizing a series of inhibitors of histone phosphate metabolism we plan to probe the role of metaphase histone phosphorylation in chromosome condensation during mitosis. We wish to extend our recent observation of an extremely rapid turnover of histone acetate, to identify the sites involved, and to isolate mutants deficient in acetylation so that the biologic function of this modification can be probed. (2) We plan to study the mode and sites of histone deposition onto the replicating chromosome, particularly directing our investigation towards a test of the idea that newly synthesized histones are not deposited upon newly replicated DNA. (3) We wish to pursue our studies of chromosome structure attempting to devise strategies of analyzing for the existence of histone oligomers in native chromatin using gentle dissociation by protamine displacement followed by analysis on neutral pH gels.